1. Field of the Invention
The invention relates to an array substrate and a fabrication method thereof, and more particularly, to use of a laser ablation process to manufacture the array substrate.
2. Description of the Related Art
LCD operation, in which angles of liquid crystal molecules are changed to control light transmission, conventionally requires a liquid crystal layer disposed between a color filter substrate and a thin film transistor (TFT) array substrate. As shown in FIGS. 1A-1E, TFT array substrate fabrication comprises five photo mask processes. The substrate is defined to two areas, with area I serving to form a TFT and area II serving a storage capacitor. FIG. 1A shows a metal layer formed on the substrate 10 and patterned by a first photo mask, thereby forming a gate electrode 11A in area I and a bottom electrode 11B in area II, respectively. As shown in FIG. 1B, a dielectric layer 12, a semiconductor layer, and a doped semiconductor layer are sequentially formed on the structure and patterned by a second photo mask, thereby forming a channel layer 13 and an ohmic contact layer 14 in area I. As shown in FIG. 1C, a metal layer is formed and patterned by a third photo mask to form source/drain electrodes 15. The channel layer 13 and ohmic contact layer 14 not masked by the source/drain electrodes 15 are etched simultaneously. As shown in FIG. 1D, a passivation layer 17 is formed and patterned by a fourth photo mask to form a contact hole 16 to expose the part of the drain electrode 15 of the TFT. A conductive layer is formed overlying the structure and patterned by a fifth photo mask. As shown in FIG. 1E, the patterned conductive layer 18 serves as a top electrode in area II and pixel electrode electrically connects to the drain electrode 15 through the contact hole 16.
In addition to the lithography process, organic or inorganic material layers can be patterned by laser ablation such as disclosed in U.S. Pat. No. 6,933,208 B2. Because the laser ablation cannot selectively pattern, it is necessary to use a photo mask, thereby raising costs. Compared to other lithography light sources, large area exposure is difficult in laser source. The photo mask alignment also complicates the machine integration. Accordingly, a selective laser ablation process without requiring a photo mask is called for.